1. Field of the Invention
The invention relates to silicon parts for plasma reaction chambers for processing semiconductor materials. The invention also relates to processes of making and using the silicon parts.
2. Description of the Related Art
In the field of semiconductor material processing, vacuum processing chambers are used for the etching of materials and for chemical vapor deposition (CVD) of materials onto substrates. A process gas is flowed into the processing chamber while energy, such as a radio frequency (RF) field, is applied to the process gas to generate a plasma.
An upper electrode (or “showerhead electrode”) 10 in an assembly for a single wafer etcher as disclosed in commonly-assigned U.S. Pat. No. 6,376,385 is shown in FIG. 1. The upper electrode 10 is typically used with an electrostatic chuck including a bottom electrode (not shown) on which a wafer is supported below the upper electrode 10.
The electrode assembly is a consumable part, which must be replaced periodically. Because the electrode assembly is attached to a temperature-controlled member, for ease of replacement, the upper surface of the outer edge of the upper electrode 10 has been bonded to a support ring 12. An outer flange on the support ring 12 is clamped by clamping ring 16 to a temperature-controlled member 14 having water cooling channels 13. Water is circulated in the cooling channels 13 via water inlet/outlet connections 13a, 13b. A plasma confinement ring 17 surrounds the upper electrode 10. The plasma confinement ring 17 is attached to a dielectric annular ring 18, which is attached to a dielectric housing 18a. The plasma confinement ring 17 causes a pressure differential in the reactor and increases electrical resistance between the reaction chamber walls and the plasma, thereby concentrating the plasma between the upper electrode 10 and the lower electrode.
Process gas from a gas source is supplied to the upper electrode 10 through an opening 20 in the temperature-controlled member 14. The process gas is distributed through one or more baffle plates 22 and passes through gas flow passages (not shown) in the upper electrode 10 to disperse the process gas into the reaction chamber 24. To enhance heat conduction from the upper electrode 10 to the temperature-controlled member 14, process gas can be supplied to fill open spaces between opposed surfaces of the temperature-controlled member 14 and the support ring 12. In addition, a gas passage 27 connected to a gas passage (not shown) in the annular ring 18 or confinement ring 17 allows pressure to be monitored in the reaction chamber 24. To maintain process gas under pressure between the temperature-controlled member 14 and the support ring 12, a seal 28 is provided between a surface of the support ring 12 and an opposed surface of the member 14, and a seal 29 is provided between an upper surface of support ring 12 and an opposed surface of the member 14. In order to maintain the vacuum environment in the reaction chamber 24, additional seals 30, 32 are provided between the member 14 and a member 18b, and between the member 18b and the housing 18a. 
In such a parallel plate plasma reactor, a wafer to be processed is placed on the lower electrode, and a RF plasma is generated between the lower electrode and the upper electrode, which is parallel to the lower electrode. The upper electrode has been made of graphite. However, as described in U.S. Pat. No. 6,376,977, during plasma etching, particles of graphite upper electrodes can drop onto and contaminate wafers that are being processed in the reaction chamber.
The upper electrode of parallel plate plasma reactors has also been made of single crystal silicon material. However, as described in U.S. Pat. No. 6,376,977, heavy metal impurities can adhere to the single crystal silicon during manufacture of the upper electrode. The metal impurities can cause contamination problems when the upper electrode manufactured from the single crystal silicon material is subsequently used in semiconductor device processing.
U.S. Pat. No. 5,993,597 discloses that plasma etching electrodes made of silicon generate dust due to stress and microcracks on the electrode surface during plasma etching.
In view of the high purity requirements for processing semiconductor materials, there is a need for parts, such as electrodes, of semiconductor processing apparatus that have reduced levels of metal impurities, and which can reduce contamination of semiconductor materials by such metal impurities during processing.